Towed in for the first time

After running the boat for a couple hours and starting the boat at least a half a dozen times without incident, I went to start the boat up to pull a skier and got nothing but a solenoid click before the dash shut off (the electronic dash shuts down with low voltage). All the symtoms of low voltage were there- the dash resetting, the perfect pass looping in boot-up mode, and low voltage reading at the dash gauge. Since the boat had been starting without incident all day, I thought low battery and possibly bad alternator. I knew the battery cables were clean and tight and all the connections all the way back to the starter were clean since I just did the starter and the relay a couple weeks ago.

We humbly got towed in by a jetski. When I got home the first thing I checked was the battery clamps. The clamps were clean and tight, but underneath the positive-cable clamp rubber shroud it was clear that the connection from the cable to the clamp itself was not so clean. The cable was literally white with corrosion, just about zero copper exposed to the clamp. I don't know how it ever started with this much corrosion. Cut back the cable a couple inches and wire-brushed it and the clamp, re-assembled, and she fired up instantly. Looks like the positive cable is corroded very deeply into the cable. I cut back about 5 inches and still had to wire-brush it to get clean copper. I figure the previous owner must have let it sit with water in the batt compartment at some time. I'll replace the whole cable at some point but just sharing this in case the same thing ruins anyone else's boating day.

I use No Ox on all battery and dc power connections.
Another hint: Wire brushing doesn’t get rid of the problem. Mix up some water and baking soda and dip your battery cable terminals in this solution. Keep it in there until it stops bubbling. This will neutralize the acid that crept up from your battery. You can use this mixture to clean the top of your battery but be careful not to get any inside your battery. Make sure the cell lids are on when you clean. Spread a film of NoOx on your cable terminals and battery posts, re terminate and you should be good to go. If your cable and terminals are too far gone, you will have to replace them. Make this a part of your annual maintainence and you shouldn't have any more trouble.
Kurt